1. Field of the Invention
The present invention relates to a technical field of ion migration, and more particularly to an asymmetric field ion mobility spectrometer.
2. Description of the Related Art
Asymmetric field ion migration is a new type of ion migration technique. It utilizes characteristic of mobility of charged molecular clusters varying with intensity of electrical field under the action of a strong electrical field, to identify corresponding molecules. Typically, an asymmetric field ion mobility spectrometer is composed of two parallel electrodes and a collection electrode. The parallel electrodes each have a length less than 10 mm, and a width less than 5 mm, with a spacing of 0.5 mm between them. The electrodes are formed by copper plated on two pieces of glass plates. Ionized molecules enter into the electrodes under the action of uniform gas flow, and only the charged molecules satisfying a specific condition can reach the collection electrode through a gap between the electrodes. One piece of electrode is grounded while the other piece of electrode is applied with pluses having amplitude up to approximate 1000V and a pulse width of dozens of nanoseconds, and at the same time is applied with a DC compensation voltage. Only the ions which satisfy a condition of K1×t1=K2×t2 can pass the gap, wherein K1 is an ion mobility under the strong electrical field, t1 is a high voltage pulse width, K2 is an inherent mobility under a weak electrical field, and t2 is a weak electrical field pulse width. The aim of identifying substances can be achieved by scanning the different ions released by the DC compensation voltage.
However, the above described asymmetric field ion mobility spectrometer with parallel electrode plates cannot accurately distinguish peak positions of different ions. Therefore, there is a need to have an ion mobility spectrometer having a new electrode structure.